Building prototypes with additive methods such as sterolithography and fused deposition modeling has been a hot topic lately and rightly so. But for parts that will eventually be injection molded, industry experts say it makes more sense to get injection molded prototypes. Trouble is, traditional tooling costs a lot, has long lead times, and is difficult to change.

Fortunately, a method called “rapid injection molding” quickly and inexpensively provides prototypes to test form, fit, and function — and in the same plastic selected for production. Users need only upload CAD models to an online site to get feedback on how to make designs more moldable. CNC'd aluminum molds generated from the finalized CAD provide an economical way to produce prototypes and low-volume runs. Rapid injection molding became feasible during the fairly recent automation of manual labor traditionally performed by engineers, tool makers, and machinists. A few examples show how medical device firms can take advantage of this technique.

User-friendly ultrasound

“When developing our first product, we were unaware of tooling options,” says Spencer Newman, president of medical-device manufacturer Newman Medical, Lake Bluff, IL, (www.newman-medical.com). “We thought our prototyping stage was complete, so we had expensive steel molds made. Turned out they needed design changes. But when it comes to steel molds, little changes often carry big price tags. That was a hard-learned lesson. Fortunately, we found rapid injection molding.”

An example application is the company's BabyBeatDoppler, a fetal ultrasound device for home use. “In the past, ultrasound was a relatively complex procedure performed in a doctor's office,” says Newman. “Now doctors often tell families to rent a system for home use. But most ultrasound equipment has a cold, clinical look. Our goal was to develop a user-friendly device intended for mothers, not healthcare professionals.”

Like most current medical devices, the ultrasound unit has many plastic components. Newman says as a non-plastics expert, he appreciated the personalized feedback from rapid injection molder Protomold in Maple Plain, MN, (protomold.com) and its online quoting engine ProtoQuote.

“The company provides free design analyses,” says Newman. “We submitted designs well before we were ready for a prototype. The company gave us detailed responses on our designs overnight. The service certainly won't replace our engineers, but it does help stretch our design budget.

Most ultrasound systems are similar in design, says Newman. “They use a sensor head consisting of transmitters and receivers. The head is placed against an expectant mother's belly to detect the fetus's heartbeat. We targeted the head geometry as the logical place to improve the design. Additive processes such as SLA or FDM wouldn't work well because their layering techniques can leave voids in finished parts. That might not matter much in some applications, but voids adversely affect ultrasonic properties. We needed prototypes as solid as injection-molded parts,” he says.

To this end, Newman's company used Protomold's sister division, First Cut. It produces prototypes directly by milling blocks of solid material. The milled parts are similar to molded parts, but milling costs less for users needing just a few copies each of a number of configurations.

“We narrowed our choices to a few different angles for transmitting and receiving signals, and wall and cavity configurations. The technique's low cost let us test several feasible designs. A finalized design cleared First Cut to go into low-volume production for us,” says Newman.

Stem cells from fat tissue

Few realize that fat tissue harbors numerous adult stem cells. In fact, fat or adipose tissue contains over 10 times the number of stem cells as an equivalent amount of bone marrow, along with regenerative cells. Collectively, these cells can promote blood-vessel growth in an injured area of the body as well as change into many tissue types including bone, cartilage, and skeletal muscle.

In most stem-cell procedures, doctors remove a small number of cells from the body and send them to a processing facility where many thousands of copies of the same cell are grown to increase the cell dosage. This takes a lot of time and costs a lot.

To solve this problem, Cytori Therapeutics Inc, San Diego, (cytoritx.com) developed the Celution device that removes and concentrates stem cells found in a patient's fat tissue. Physicians can reintroduce them into the patient's body, bedside, in about an hour. This eliminates the growing and transportation of cells, as well as tissue-matching problems.

Celution consists of a reusable drive mechanism and single-use therapeutic sets or cage-like plastic components lined with mesh to capture tissue. The company says an Internet search turned up Protomold as a prototyping option. “Based on the device's expected sterilization process and operation, our development team needed a strong material with high heat and high chemical resistance that wouldn't leach out plasticizers as some resins do,” says development engineer Bobby Byrnes. “We also had to make sure the device was biocompatible and could stand up to the rigors of international shipping even after sitting in a warehouse a long time. Making development more difficult were separate approval processes for regulatory bodies in the United States, Europe, and Japan, all of which require validated parts,” he says.

The company submitted its CAD design to the ProtoQuote online quoting system. “Basically, our design worked, but the modifications ProtoQuote suggested were a big help. After making the changes, we requested and got a three-day turnaround. We had five different disposable components prototyped in this way. The parts worked so well, we immediately went into production for clinical trials.”

Tips for selecting a prototyping partner

What is the best way for selecting an injection molder? A good first step is to ask colleagues for recommendations. An online search might be useful to see how the companies promote themselves. A few more questions to ask include:

How fast can the company make and ship parts? Compressing your design cycle partially depends on the speed of the supplier. Some organizations say they can ship tens to thousands of parts within a few days from receipt of your 3D CAD model.

Can the company quickly provide quotations on-line? Some firms have quoting engines on their Web sites. Users fill in a form and get an instant estimate. Within reason, it's actually less important how fast you get an estimate than what you get with the numbers. Is the information helpful? Does the quoting engine include adjustable parameters so you can tweak specifications and evaluate how this affects price? Does the site include design guidelines?

Does the company provide technical assistance? You should be able to communicate with the injection molder's engineering staff if you need assistance. Questions regarding part moldability or material requirements should be discussed early in the prototyping process.

The company should electronically accept 3D CAD files in several standard formats and the most commonly used native formats. To keep data-management issues straight, the firm should also provide version control and archiving capabilities in-house.

Can the company predict mold-flow issues in a timely manner? Is there an extra charge for the service? Flow simulations can find potential flow problems before prototyping begins.

Has the company done work similar to what you are asking? Check its Web sites for case studies, testimonials, and other verifications of expertise. Track records will help flush out firms that claim they deliver but have problems following through. Does the firm's Web site have intuitive self-help tools such as account portals, libraries, and technical archives? Does the site convey the company's expertise, talent, and capabilities effectively? Can you easily contact sales and customer service?

Does the company act as a broker? This isn't necessarily bad, but a broker's main function is to take your specifications to other injection molding companies with which they have agreements. Brokers typically get one or more bids on a job, choose molders they believe appropriate, and then send you what they think is a best bid. Brokers receive fees or commissions. Less-than-honest firms have been known to recommend the highest-paying commission bid.

That said, honest brokers can add value several ways. Some can help compare and contrast prototyping processes, provide design expertise, or provide materials advice. Still it's best to ask upfront whether the firm acts as a broker. Some brokers never mention they don't manufacture parts in-house, and some strongly imply they do, when, in fact, they don't. Should something go wrong, it might be difficult to get the problem resolved. — L.G.

Many are the advantages

Companies that provide rapid injection molding tout advantages such as:

• Aluminum tooling that typically costs a fraction of traditional multicavity steel molds. This delays a larger investment and improves cash flow. It also eliminates committing to large production volumes to amortize tooling costs.

• Rapid tooling allows for design changes almost right up to the last minute. In contrast, conventional tooling often requires “freezing” design to accommodate long lead times.

• Rapid injection molding provides a handy “bridge” from low to high-volume production.

• Companies are less likely to get stuck with inventories to store, ship, or recycle should problems arise. — L.G.